Kurt Poulsen 2020/09/27 12:06

Hi All

I have got direct mail and messenger messages about an image in the report about calibration of the SAA-2N I published a couple of days ago.

It is a picture of an uncalibrated sweep of the VNA-QT software causing people to start comparing uncalibrated dynamist range. So her is a contribution the raise some understanding of what it is all about.

Before I start on my lecturing 😊 please be aware I am working on a similar report for the various SAA2 versions with SMA adaptors for the well known SMA calibration kit supplied with these products

Here it comes………….

Sorry to say, it makes no sense to compare these uncalibrated measurements.

I have apparently been the one providing a single image in my document being an uncalibrated sweep kicking off this discussion.

Please understand that any comparison must be done after a calibration as anything connected to port 1 and port 2 such as adaptors and test cables are an integral part of the NanoVNA or SSA-2 of any brand or type or manufacture.

An example is the SAA-2N which internally are fitted with SMA connectors and thus fitted with SMA male to N female adaptor and this will change the uncalibrated response considerable.

Another example is my test setup shown in the picture attached where my SAA2 purchased from Tindie (and wrapped in a green plastic box bought from Germany) where I have a SMA to APC7 adaptor (APC7 ha no male or female part, they are sexless) fitted so I can exchange from my professional HP calibration adaptors of any gender male and female as APC7 to SMA and N adaptors. These adaptor are not having any PTFE/Teflon insert but are airline type and the SMA and N adaptors are with strict mechanical dimension ,so when I characterize calibration kit items, like I did for those N SOL adaptor in my document as I recently published, and the reason for the "ugly" uncalibrated image, then they are actually an accurate clone of the professional SOL master calibration kit. Even then I do a mathematical process to clean the measured data for noise.

So please understand first when any VNA type is calibrated with my professional calibration kit, you will see the real performance and only then all inclusive.

When using a random calibration kit e.g. the set delivered with the SAA-2N, and using my calibration data you get as close you can, but still there are deviation as you kit has mechanical and thus electrical deviation to my characterized similar kit.

It will mainly be the load having some deviation but the female N will also as the center conductors length will differ from my Professional HP female kit. Just study the manufacturers N female mechanical specifications and you will see considerable tolerances. However I have described how to compensate for this open cal standard issue by sweeping the suppled male ale test cable and fine tune the calibration.

Summary: You will confusing more than helping issuing comparing of these useless uncalibrated measurements, so my recommendation is do not do it
Kind regards